In Part 1 §7 of "The Principles of Human Knowledge", Berkeley declares: "From this it is evident there is not any other substance than SPIRIT, or that which perceives". I shall attempt to trace out the chain of reasoning which leads him to this startling conclusion.
Berkeley begins with an inventory of 'the objects of human knowledge', or equivalently, ideas. Berkeley's use of the term 'idea' seems to correspond with Locke's, for whom ideas denote "the Object of the Understanding when a Man thinks ... or whatever it is, which the Mind can be employ'd about when thinking". Ideas are objects of acts of thinking; so whenever one perceives or imagines, one perceives or imagines something, and this something is the object of the thought, or the idea. Moreover, this act model of the operations of the mind requires the existence of an agent, who operates on the objects of thought, "something which knows or perceives them". Berkeley says that the agent who performs operations on ideas, such as willing, imagining, and remembering, is variously referred to as 'mind, spirit, soul, or myself'.
Berkeley goes on to note that our ideas of sensible objects are complex, in two ways. Firstly, an idea of a sensible object is composed of a number of different ideas, which give the object's ...
The solution summarizes and explains Berkley's arguments for immaterialism.